Android TalkBack support

[JRJurman]

After #29 , I believe the last remaining major screen reader to add support for would be Android TalkBack. I have a plan to do this work, but probably won't be able to dedicate time to this until next week (late April).

[m1maker]

Okay. However, please don't call it SRAL_ANDROID_TALKBACK or something like that. Consider doing this through the accessibility manager (it seems that's what it's called in Android). Then he will be able to talk to all the normal screen readers that support this. Then it can be called, for example, SRAL_ANDROID_SCREEN_READER.

[JRJurman]

Completed as part of #31